Cal Tech Announces Joint Search for Gravitational Waves

California Institute of Technology News Release

2007 February 13

PASADENA, Calif. and CASCINA, Italy - The Laser Interferometer
Gravitational-Wave Observatory (LIGO) and the Virgo interferometric
gravitational-wave detector of the European Gravitational Observatory (EGO) near
Pisa, Italy, have agreed to join in a collaborative search for gravitational
waves from sources in and far beyond our galaxy. The collaboration will link the
three LIGO detectors, which are in the United States, and LIGO's partner, GEO600
in Germany, with the Virgo detector to increase the likelihood of detecting the
elusive phenomenon first predicted over 90 years ago by Albert Einstein in his
general theory of relativity, and pinpointing the source of the signals.

LIGO is funded by the U.S. National Science Foundation, Virgo is funded jointly
by the Italian Istituto Nazionale di Fisica Nucleare (INFN) and the French
Centre National de la Recherche Scientifique (CNRS) through the EGO Consortium,
and GEO600 is funded jointly by the Max Planck Society in Germany and the
Particle Physics and Astronomy Research Council in the United Kingdom. Peter
Saulson of Syracuse University, spokesperson for the LIGO Scientific
Collaboration, and Benoit Mours of the Laboratoire d'Annecy-le-Vieux de Physique
des Particules, spokesperson for the Virgo Collaboration, guided the discussions
that brought about this agreement. The LIGO and Virgo collaborations have
collaborated in the past on more limited technical investigations, but this
agreement is the first to involve full data sharing.

"This is a landmark agreement," Saulson says. "The members of both
collaborations have overwhelmingly embraced this effort, recognizing that in
spite of the hard work that it will take, the best science will come from
collaboration."

LIGO, in the midst of a nearly two-year run functioning at its design
sensitivity, is operating along with GEO600, while Virgo is making rapid
progress toward its sensitivity goals. The agreement calls for data sharing to
begin when the sensitivity and duty cycle of the interferometers allow a
significant contribution to joint searches for gravitational waves. In the
meantime, the two collaborations have begun to merge some of their data-analysis
activities in anticipation.

Mours described the importance of this agreement. "Combining the data from the
collaborations is a classic example of 'the whole being more than the sum of the
parts.' The combined data will give us a much better chance of finding the first
gravitational waves, and will allow us to have greater confidence in any
detections. And, if we find something, the combined data will provide more
information about the location of the source than either project alone could."

LIGO operates laboratories in Livingston, Louisiana, and Hanford, Washington.
The project was designed and is operated by the California Institute of
Technology and the Massachusetts Institute of Technology. Research is carried
out by the LIGO Scientific Collaboration (LSC), a group of 500 scientists at
universities around the United States and in eight foreign countries.

The LSC includes the members of GEO600, the German-British project that operates
an interferometer near Hannover, Germany. Data from the GEO600 interferometer
have been used in a number of observations by the LSC, and are expected to
continue to play an important role in the global network once Virgo joins.
Bernard Schutz, representing GEO, welcomes Virgo's participation. "With this
agreement we are pioneering a closer level of scientific cooperation between the
USA and Europe. By completely pooling our data and coordinating our operations
we greatly improve the sensitivity of all our detectors and agree to share
equally in the scientific results of our hard work. Science is the big winner
from this agreement."

The Virgo Collaboration comprises 180 scientists from 13 institutions in France,
Italy, and the Netherlands.

This agreement lays the groundwork for future expansion of worldwide
collaboration. It explicitly states that new detectors are welcome to join the
international network of gravitational-wave detectors as the new detectors
become operational at a sensitivity that would benefit the collective scientific
capabilities of the network.

The LIGO, GEO600 and Virgo detectors are very similar in concept, though many
aspects of the apparatus have different detailed implementation. All projects
have L-shaped facilities with multi-kilometer-long arms (4 kilometers for LIGO,
3 kilometers for Virgo, 600 meters for GEO600) with evacuated tubes that contain
laser beams monitoring the positions of precision mirrors using interferometry.
According to Einstein's theory, the relative distance of the mirrors along the
two arms changes very slightly when a gravitational wave passes by. The
interferometers are set up in such a way that a change in the lengths of the
arms as small as one part in ten to the 18th meters (a thousandth the diameter
of an atomic nucleus) can be detected.

The next major milestone for LIGO, Advanced LIGO, funded by the National Science
Foundation with British and German partners, is expected to start construction
in 2008. Advanced LIGO, which will utilize the infrastructure of LIGO, will be
10 times more sensitive than the current LIGO detectors. Virgo scientists are
also planning for a comparable upgrade of their detector (Advanced Virgo), which
will be made about the same time.